| name | gasket-design |
| description | Gasket design — ASME PCC-1/ASME VIII gasket seating, gasket factors (m and y), bolt load calculations, spiral wound/ring joint/sheet gaskets, face finish requirements, leak tightness, flanged joint assembly, ASME B16.20. |
| metadata | {"priority":7,"promptSignals":{"phrases":["gasket design","flanged joint gasket","ASME gasket","gasket seating stress","spiral wound gasket","bolt flange gasket"],"minScore":3}} |
Gasket Design — Complete Skill
Gasket Fundamentals
Gasket function: deformable material between flange faces; fills face irregularities; maintains seal under differential pressure
Seating requirement: sufficient bolt load to seat gasket (plastic deformation → fill surface asperities)
Service requirement: bolt load must exceed: gasket seating stress + pressure-induced load + external loads
Gasket area:
A_g = π/4 × (G_o² - G_i²) [mm²; G_o = outer gasket diameter; G_i = inner gasket diameter]
Effective gasket diameter G: G = (G_o + G_i) / 2 for most configurations
ASME Section VIII Appendix 2 — Flange Design
Gasket Factors m and y
m (gasket factor): dimensionless; minimum seating stress under operating pressure relative to internal pressure
p_min_operating = m × P [MPa; m = gasket factor; P = design pressure; p_min_operating = required contact pressure]
y (minimum seating stress): minimum stress required at assembly to seat gasket (before pressure)
y [MPa] = minimum bolt-up contact pressure
ASME Appendix 2 gasket factor table (selected):
| Gasket Type | m | y [MPa] |
|---|
| Rubber (durometer 75) | 1.0 | 1.4 |
| Full-face soft rubber | 0.5 | 0.2 |
| Spiral wound metallic — carbon steel | 3.0 | 69 |
| Spiral wound metallic — stainless | 3.0 | 69 |
| Metal ring joint (oval/octagonal) | 5.5 | 179 |
| Corrugated metal — SS | 3.75 | 52 |
| Flat metal (SS, full contact) | 6.5 | 207 |
| Compressed asbestos (now replaced) | 2.0 | 11 |
Bolt Load Requirements
Operating condition bolt load:
W_m1 = π/4 × G² × P + 2b × π × G × m × P [N; b = effective gasket seating width; G = mean gasket diameter]
Or simplified: W_m1 = π G² P/4 + 2πGbmP = π G P (G/4 + 2bm)
Seating condition bolt load:
W_m2 = π G b y [N; y = seating stress [MPa]; b = effective gasket width [mm]; G = mean gasket diameter [mm]]
For wide gaskets (N > 12.7 mm): b = 2.53 × √N where N = gasket width [mm]; N/2 otherwise
Design bolt load: W_design = max(W_m1, W_m2)
Bolt load per bolt:
F_bolt = W_design / n_bolts [N]
Bolt torque: T_bolt = K × F_bolt × d_bolt [N·mm; K = torque coefficient ≈ 0.15–0.20 with lubrication; d_bolt = bolt diameter]
Bolt Area Check
Required total bolt area:
A_m = max(W_m1 / S_b, W_m2 / S_b) [mm²; S_b = bolt allowable stress at operating temperature [MPa]]
Select bolts: Σ A_bolt_actual ≥ A_m
Available bolt load (full torque):
W_available = A_bolt_actual × S_b [N; should exceed design bolt load by ≥ 10%]
Gasket Types
Spiral Wound Gaskets (ASME B16.20)
Construction: V-shaped metallic strips (SS, Monel) alternating with filler (PTFE, graphite) wound in spiral
With inner ring: controls compressibility (prevents over-compression); required for ASME B16.5 Class 600+
With outer ring (centering ring): locates gasket on flange; prevents blow-out; required for Class 900+
Color code: winding material coded; SS with PTFE filler = blue outer ring (standard)
Seating: m = 3.0, y = 69 MPa (ASME values; some manufacturers specify different — follow data sheet)
Face finish requirement: serrated (250–500 μin AARH Ra); smooth finish reduces seating effectiveness
Applications: refinery piping; chemical processing; high-temperature steam (up to 650°C with graphite filler)
Ring Type Joint (RTJ) Gaskets (ASME B16.20)
Types: oval (BX, R-type); octagonal (most common for high pressure)
Material: soft iron (316 for SS flanges); softer than flange material (critical)
Applications: API 6A flanges; wellhead; high pressure (Class 600–2500); high temperature
Seating: m = 5.5; y = 179 MPa; requires high bolt load → heavy flanges required
Groove: precision-machined groove in flange; RTJ gasket contacts groove flanks only (not groove base)
Full-Face Gaskets
Used with: flat-face flanges (cast iron, ductile iron; non-metallic)
Configuration: bolt holes punched in gasket; gasket covers full flange face
Advantages: distributes bolt load uniformly; prevents flange bending (critical for brittle materials)
Effective area: smaller than physical area due to bolt holes; must calculate A_eff carefully
Compressed Non-Asbestos (CNA) Sheet Gaskets
Materials: graphite/PTFE composite; aramid fiber; nitrile rubber (NBR) bound; carbon/glass fiber
Applications: water/steam <200°C; HVAC; low-pressure process piping
Gasket factor: m ≈ 2.0–3.5; y ≈ 25–50 MPa (lower than metallic)
Cut: laser-cut or water-jet; ensures consistent dimensions and area
Flange Face Finish
Serrated finish (concentric): 125–250 μin AARH (arithmetic average roughness) Ra ≈ 3–6 μm
Smooth finish: 63–125 μin AARH; for elastomeric gaskets
Stock finish: 250–500 μin AARH; for metallic spiral wound (serrations interlock with windings)
Phonographic finish: spiral serrations 1/16 in/rev; legacy term for concentric equivalent
Face roughness check: profilometer measurement; acceptance per ASME B46.1 and PCC-1
Leak Tightness Assessment (ROTT/PVRC Method)
Pressure × Width parameter:
Tp = P × G / (2b) [MPa; leak tightness parameter; based on enhanced ASME method]
PVRC (Pressure Vessel Research Council) Tightness-based design:
L_class: Tp must exceed threshold for required tightness class (L0.01: moderate; L0.001: tight; L0.0001: very tight)
Accounts for gasket load relaxation and pressure cycling
Assembly and ASME PCC-1
ASME PCC-1 (Guideline for Pressure Boundary Bolted Flange Joint Assembly):
Bolt tensioning sequence:
- Hand-tighten all bolts
- Star pattern torque: 30% → 60% → 100% target torque → final check (all bolts at 100%)
- For Class 600+: use hydraulic bolt tensioners; 4-bolt simultaneous tensioning
Bolt stretch measurement: preferred over torque; avoids torque-friction uncertainty
Target bolt stress: 40–70% of bolt yield strength (not more → limits embedment at assembly)
Gasket stress after assembly relaxation:
σ_g_final = σ_g_initial × (1 - e^(-t/τ)) [gasket creep relaxation; τ = relaxation time constant from test data]
For graphite spiral wound: 15–25% stress loss in 24 hours; must design with relaxation margin
Standards
| Standard | Scope |
|---|
| ASME Section VIII Appendix 2 | Flange and gasket design rules |
| ASME B16.20 | Metallic gaskets for pipe flanges (spiral wound, RTJ) |
| ASME B16.21 | Nonmetallic flat gaskets for pipe flanges |
| ASME PCC-1 | Bolted flange joint assembly guideline |
| ASME B16.5 | Pipe flanges and flanged fittings |
| EN 1591-1 | Flange joints with gaskets — calculation |
Output
Provide: gasket type (spiral wound/RTJ/CNA), material and filler, gasket dimensions (G_o, G_i, G, b [mm]), gasket factors m and y (ASME table), operating pressure P [MPa] and temperature [°C], W_m1 [kN] and W_m2 [kN], design bolt load W_design [kN], number of bolts and bolt size, bolt torque T_bolt [N·m] (K-factor used), actual bolt area Σ A_bolt [mm²] vs. required A_m [mm²], gasket contact stress σ_g [MPa] at assembly and operating, face finish specification [μin Ra], assembly sequence (PCC-1 torque pattern), leak tightness class, and applicable standard (ASME VIII App. 2, ASME B16.20, ASME PCC-1).
